In the preparation of strands, threads, yarns and the like (hereinafter "bundles") it is often required that the fibers, which make up the bundles, be coated or treated with an appropriate size or binder to impart to the finished bundle certain desired properties. Thus, for example, in the preparation of a bundle of glass fibers that are to be used to reinforce a resin matrix it is common practice to place on the fibers that form the bundle a binder that will impart to the glass fiber bundle an affinity in the bundle to firmly bond the glass bundle reinforcement to the resin matrix that is being reinforced. The binders or sizes used are applied by spray devices, pads and in the case of glass fibers most commonly from the surface of applicators of the roller or belt type. Regardless of the apparatus used to place the binder or size on the fibers making up a bundle, the amount of that size or binder can vary over a wide range depending on circumstances. The quantity of binder or size can often be a critical factor in determining whether or not a given bundle is satisfactory for its intended use. In determining what that quantity is, a large length, typically 120 yards of the bundle to be tested in the case of a fiber glass bundle, is collected and weighed. The bundle is then subjected to the application of heat to burn off the binder material therein, and it is then subjected to further weighing. The difference in the weights obtained is the LOI of the bundle when it is divided by the original weight and multiplied by 100.
As will be appreciated by the skilled artisan, this is a costly and time consuming test and in many instances provides information that is of little practical value since, if corrections need to be made to the manufacturing process, they are made only after many yards of defective materials have been formed. In many instances where the LOI for a given fiber bundle exceeds that of the specification for the product but does not interfere with the performance of the product, that excess represents increased manufacturing costs while not providing any benefit to the user. This is an unacceptable practice for the manufacture if it can be controlled or avoided. The difficulty in making the rapid measurements necessary to address the problems referred to reside in the fact that the fibers which constitute the bundles have the binder applied to them as they are being formed and the bundles are moving as they are formed at high speeds. By "high speeds" as used herein in the specification is meant a linear movement of the bundles typically speeds of 2,500 to 20,000 feet per minute or more. The binders and sizes are added to the fibers usually as they pass over an applicator or through the spraying zone as the case may be while they are moving at high speed and it is difficult to ascertain the accuracy of the application of the material to the fibers without going through the time consuming weighing procedure which has been described generally above.
Thus, a need exists for a reliable and rapid method and apparatus for determining the LOI on bundles being produced from a plurality of fibers. This need is especially required in the formation of fibers used to form glass fiber bundles to assess accurately the operation of the applicators in that art and their effectiveness in delivering to the fibers the desired or required amount of binder or size. The instant invention satisfies these needs.